Process for decomposing hydrogencontaining gas mixtures



Dec. 6, 1960 M. SEIDEL 2,962,867

PROCESS FOR DECOMPOSING HYDROGEN-CONTAINING GAS MIXTURES Filed Aug. 5, 1957 2 Sheets-Sheet 1 Fig.1

Dec. 6, 1960 M. SEIDEL 2,962,867

PROCESS FOR DECOMPOSING HYDROGEN-CONTAINING GAS MIXTURES Filed Aug'. 5, 1957 2 Sheets-Sheet 2 F I'gQ 2 United States Patent PROCESS FOR DECOMPOSING HYDROGEN- CONTAINING GAS MIXTURES Max Seidel, Munich-Solln, Germany, assignor to Gesellschaft fiir Lindes Eismaschinen Aktiengeseilschaft, Hollriegelskreuth, near Munich, Germany, a German company Filed Aug. 5, 1957, Ser. No. 676,112

Claims priority, application Germany Sept. 20, 1956 7 Claims. (Cl. 62-20) It is known to prepare hydrogen and hydrogen-nitrogen mixtures from hydrogen-containing gas mixtures, particu larly coke over gas, by first condensing out the more difficultly volatile components, for example lower aliphatic hydrocarbons and then separating out the bulk of the more easily volatile components methane, carbon monoxide and nitrogen at a low temperature. The remaining carbon monoxide which can be condensed out only with difiiculty is subsequently washed out of the gas mixture with liquid nitrogen. The nitrogen content of the nitrogen-hydrogen mixture collected after the washing depends on the washing pressure and the washing temperature. In selecting these conditions it is to be noted to what extent the carbon monoxide in particular must be removed. In order to produce the coldness required for the washing process, more nitrogen is liquefied than would actually be required for the washing. Nitrogen, compressed at room temperature to high pressure, for example 180 atmospheres, is cooled by counter-current contact with cold decomposition products and is then expanded and liquefied. A part is expanded only to the washing pressure, the other part, used as refrigerant, to a lower pressure. A closed nitrogen refrigerating cycle has also been used already. It is disadvantageous that large quantities of nitrogen must be compressed to high pressure.

In order to avoid the high pressure nitrogen cycle, it has already been suggested to take liquid nitrogen from an air decomposing installation and to wash the hydrogen-containing gas mixtures with it, the coldness required for the Washing being taken from the air decomposing installation. The pressure to be used in the washing however lies above the pressure which is sufiicient for air decomposition. The entire quantity of air to be decomposed must therefore be compressed to a higher pressure; this is not economical. Moreover the gas mixture decomposition installation is freely and openly connected with the air decomposition installation, through pipe lines, so that explosive gas mixtures can occur. Moreover the cold balance of the cold exchangers in the air decomposition installation is disturbed, since one product, namely the nitrogen, is withdrawn in liquid form; its cold content is not available for the cooling of the air to be decomposed. More warm air flows into the cold exchangers than cold decomposition products flow out through them.

The procedure according to the present invention does not possess the described disadvantages. The invention refers to a procedure for the decomposition of hydrogencontaining gas mixtures, particularly coke over gas, in which the difiicultly condensible components of the gas mixture are washed out with liquid nitrogen, won by an air decomposition procedure in which this nitrogen is produced from gaseous nitrogen compressed at room temperature to high pressure, cooled in counter-current with itself and with components of the gas mixture. The characterizing feature of the invention consists in that the cooled nitrogen is liquefied at least partly by indirect heat exchange with cold air that is to be decomposed.

2,962,867 Patented Dec. 6, 1960 Any desired amounts of air can be decomposed in the air decomposition installation, although the air and gas mixture decomposition installations are functionally connected with each other. The air decomposition installation can therefore be dimensioned for large amounts of air; it can be equipped with expansion turbines which may be inserted with good economy only in cases of large outputs. Into the air decomposition installation flows the same quantity of air, by weight, as decomposition products flow out. The pressure under which the air is rectified is independent of the washing pressure; therefore it is not necessary to compress the entire quantity of air to be decomposed to the washing pressure. There is no free, open connection between the air and the gas mixture decomposition installation. Nevertheless the air decomposition installation serves as source of cold whereby the coldness of cold air to be decomposed is withdrawn. It is however not withdrawn from cold oxygen and also not from cold nitrogen. The cold economy of the cold exchangers in the air decomposition installation is therefore always balanced.

In an air decomposition installation which is equipped with a double rectification column, a part of the cold air to be decomposed can be blown directly into the upper column, which is under approximately atmospheric pressure. In the procedure according to the invention use is made of this mode of action in two difierent ways. In the one way the cooled nitrogen intended for the washing is liquefied at least partly by indirect heat exchange with liquid air enriched with oxygen whereby a part of this enriched liquid air is evaporated. The liquid gas mixture can then be decomposed in the upper column into pure nitrogen and pure oxygen. In the other method the cooled nitrogen is liquefied at least partly by indirect heat exchange with gaseous air cooled to condensation temperature and subsequently to be expanded, for example in a turbine, to approximately condensation temperature, whereupon it is led directly into the upper column.

The hydrogen-nitrogen mixture formed in the washing process usually does not yet have the desired composition. It is already known to add liquid nitrogen. It is however more advantageous to make the amount of washing nitrogen only so small that the mixtures are sufficiently purified, and if necessary to add any nitrogen still required for the desired hydrogen-nitrogen ratio only to the mixture formed by the washing after it is again heated.

If hydrogen is to be produced, then liquid nitrogen must be evaporated in indirect heat exchange with the washed gas mixture under a pressure which lies below the Washing pressure. Only in this Way can a temperature be achieved which is sufliciently low to completely condense the nitrogen remaining in the hydrogen. The required liquid nitrogen is withdrawn from the washing nitrogen and evaporated in indirect heat exchange with the gas mixture to be purified, under negative pressure.

A device for carrying out the procedure according to the invention consists in its main parts of a coke over gas producer and an air decomposition installation. Both installations have their own insulating envelopes and are connected with each other through two insulated lines. The one line serves for cold gaseous washing nitrogen, the other serves for at least partially liquefied washing nitrogen. The cold losses would however be somewhat less if both installations were insulated in common. But separate insulations have the advantage that no explosive gas mixtures can form in the insulating envelopes even when, for example, a flange or packing box becomes leaky. For the same reason it is also more expedient to introduce washing nitrogen into the air decomposition installation, instead of charging liquid or cold gaseous air into the coke oven gas installation.

In order that the washing nitrogen can be liquefied by heat exchange with liquid air, there is an evaporating condensor arranged in the air decomposition installation, which on the exaporator side, has liquid air enriched with oxygen flowing through it, which flows from the foot of the lower column to the upper column of a double rectification column. If on the other hand the washing nitrogen is to be liquefied by indirect heat exchange with cold gaseous air, then a heat exchanger is arranged in the air decomposition installation, for washing nitrogen on the one hand and gaseous cold air on the other hand, which is subsequently expanded in an expansion turbine and then blown into the upper column of a double rectification column.

Two examples of the procedure according to the invention are represented diagrammatically in Figures 1 and 2. All auxiliary equipment which is not significant to the invention, such as an ammonia pre-cooler, gel drier, filter, super-cooling devices, cO -separating devices, separating devices for higher boiling materials etc. are not shown. The same or similar parts of the two figures are designated by the same number; lines, valves etc. are designated with single numbers; the apparatus of the air decomposition installations are designated by numbers starting with 11, and those of the gas decomposition installation by numbers starting with 21.

Fig. 1 shows a suitable combination of a gas decomposition installation for the preparation of a hydrogennitrogen mixture with an air decomposition installation with a counter-current pipe system as heat exchanger and with a rectification column, in front of which is connected an expansion machine.

The air decomposition installation consists of the compressor 11, the heat exchanger 12, the expansion machine 13, the liquefier 14, the pressure column 15, the upper column 16, the air entrance line 1, the exit line for pure nitrogen 2 and the exit line for oxygen 3.

The gas decomposition installation consists of the higher pressure nitrogen compressor 21, the heat exchangers 22 and 23, the washing column 24, the heat exchanger 25, the residual gas evaporator 27, the crude gas entrance line 5, the nitrogen exit line 6, the residual gas exit line 7 and the expansion valves 8.

Both installations are connected through the heat exchanger 31, which in this case is an evaporator condensor.

The air for the air decomposition installation is com pressed by the compressor 11 to for example 26 atmospheres absolute pressure, cooled in the heat exchanger 12 and then divided into two streams. The one stream is liquefied in the liquefier 14, and then expanded into the pressure column 15. The other stream is expanded in the expansion machine 13, yielding work, and then likewise led into the pressure column 15. The oxygenenrichecl liquid collecting at the foot of the pressure column 15 is expanded and then led through the heat exchanger 31, where it evaporates partially. On the basis of this evaporation so much heat is withdrawn from the compressed and cooled washing nitrogen flowing in from the gas decomposition installation in an indirect heat exchange, that it is liquefied. From the heat exchanger 31 the oxygen enriched liquid-vapor mixture arrives in the upper column 16. Here it is Washed with the liquid nitrogen expanded from the pressure column 15 into the head of the column 16, and decomposed into pure nitrogen and impure oxygen. Both products are led out of the upper column 16, giving off coldness, through the liquefier 14 and the heat exchanger 12. The impure oxygen is led off through the line 3. The pure nitrogen arrives through the line 2 at the high pressure nitrogen compressor 21 of the gas decomposition installation. The Washing nitrogen is compressed here to for example 200 atmospheres, subsequently cooled in the heat exchangers 22 and 23 and expanded in the expansion valves 8 up to from 16 to 17 atmospheres absolute pressure and then liquefied in the heat exchanger 31 and then led into the washing column 24 at the top.

The crude gas entering at 5 under a suitable pressure of for example 15 atmospheres absolute pressure arrives through the heat exchanger 25 and the residual gas evaporator 27 at the bottom of the Washing column 24, in which the liquid nitrogen runs down and washes out the contaminations. The pure gas leaving at the head of the washing column 24 gives up its coldness in the heat exchanger 25 to the crude gas and the heat exchanger 23 to a part of the high pressure nitrogen and leaves the installation at 6. Nitrogen, possibly still lacking for the desired mixture composition can be added to the line 6 directly through a line from the high pressure nitrogen compressor 21. The residual gas becomes heated in the heat exchanger 22 in counter current to the other part of the high pressure nitrogen and leaves at 7.

Figure 2 represents a gas decomposition installation for the production of gas having a high hydrogen content. The additional coldness to be produced in this installation is withdrawn from a Linde-Frankl air decomposition installation by means of heat exchange through regenerators. 7

The air decomposition installation consists of the compressor 11, the regenerators 17 and 18, the pressure column 15, the upper column 16, the expansion turbine 13, the pipe coils 19, the air entrance line 1, the exit line for pure nitrogen 2, the exit line for oxygen 3, and the exit line for impure nitrogen 4.

The gas decomposition consists of the high pressure nitrogen compressor 21, the heat exchangers 22 and 23, the washing column 24, and the heat exchangers 25 and 26, the residual gas evaporator 27, the nitrogen vacuum evaporator 23, the vacuum pump 29, the crude gas entrance line 5, the hydrogen exit line 9 and the residual gas exit line 7.

The two installations are connected with each other by the heat exchanger 32.

The air for the air decomposition installation is compressed by the compressor 11, formed as a turbocompressor, to for example 5.6 atmospheres absolute pressure, cooled oflf in the regenerators 17 and 18, and for the most part led to the pressure column 15. A small part of the compressed air is withdrawn from the iddle of the regenerators 17 and led to the expansion turbine 13. A part of the compressed air, completely cooled down in the regenerators 17 and 18, is slightly heated again in the heat exchanger 32 by liquefying compressed washing nitrogen from the gas decomposition installation and led together with the part of the compressed air withdrawn from the middle of the regenerators 17 to the expansion turbine 13, expanded so as to yield work, and then led into the upper column 16. The pure nitrogen is drawn from the head of the upper column 16 through the pipe coils 19 to the regenerators 17 and the line 2, entirely or in part by the high pressure nitrogen compressor 21. The impure nitrogen is withdrawn through a so-called Lachmann tap between the head of the upper column 16 and the inlet point of the liquid crude oxygen from the foot of the pressure column 15, heated by the regenerators 17 and leaves the installation at 4. The oxygen from the upper column 16 leaves the installation through the regenerators 18 at 3.

The crude gas entering at 5 with a suitable pressure of for example 30 atmospheres absolute pressure arrives through the heat exchangers 25 and 26 and the residual gas evaporator 27 into the washing column 24, in which the contaminations are washed out by downwardly flowing liquid nitrogen. The nitrogen is compressed in the high pressure nitrogen compressor 21 to for example atmospheres absolute pressure, cooled in the heat exchangers 22 and 23 and thereafter liquefied in the heat exchanger 32 according to the invention in indirect heat exchange with compressed air. The one part is led after corresponding expansion into the upper part of the wash ing column 24. The other part is expanded, if necessary with supercooling, for example by hydrogen being withdrawn, into the nitrogen vacuum evaporator 28 arranged above the washing column 24. The nitrogen evaporated under vacuum is drawn through the heat exchanger 23 by the vacuum pump 29. Through the evaporation of the nitrogen under vacuum so much coldness is produced at sufiiciently low temperature, that almost all the nitr geu-down to a slight residue of for example 2%is condensed out of the hydrogen-nitrogen mixture coming from the washing column 24 and pure or almost pure hydrogen leaves the gas decomposition installation at 9, after it has given up its coldness in the heat exchanger 25 to a part of the crude gas. The liquefied residual gas is withdrawn from the lower part of the washing column 24, evaporated in the residual gas evaporator 27 by cooling crude gas and leaves the installation at 7, after its cold ness has been exchanged partly in the heat exchanger 26 with the crude gas and partly in the heat exchanger 22 with the high pressure nitrogen.

I claim:

1. Process for the decomposition of a hydrogen-containing gas mixture involving washing at least one ditficultly condensible component out of said gas mixture by contacting it with liquid nitrogen which comprises simultaneously operating a gas decomposing plant operating upon said gas mixture and an air decomposing plant, withdrawing nitrogen from said air decomposing plant, compressing the nitrogen to the pressure required for said washing operation, precooling the compressed nitrogen by indirect heat exchange with at least one fraction of said hydrogen-containing gas mixture in said gas decomposing plant, further cooling and at least partially liquifying said precooled nitrogen by indirect heat exchange in said airdecomposing plant and returning the resulting liquefied nitrogen to said gas decomposing plant and using it therein as the washing liquid.

2. Process as defined in claim 1 in which the precooled nitrogen is liquefied at least in part in indirect heat exchange with oxygen enriched liquid air.

3. Process as defined in claim 1 in which the precooled nitrogen is liquefied at least in part in indirect heat exchange with gaseous air cooled to condensation temperature and subsequently expanded to yield work.

4. Process as defined in claim 1 for the production of a hydrogen-nitrogen mixture in which the washing nitro gen quantity is made only so small that the mixture is purified sufiiciently and that nitrogen is added to the mixture formed in the washing after it has been heated again.

5. Process as defined in claim 1 for the production of hydrogen in which a portion of the liquid nitrogen is separated from the Washing nitrogen and evaporated in indirect heat exchange with the gas mixture to be purified under subatmospheric pressure.

6. Apparatus for the decomposition of a hydrogen containing gas mixture consisting of a gas decomposition plant comprising a liquid nitrogen washer for said gas mixture and a heat-exchanger for cooling nitrogen, an air separation plant, and a condensor for liquefying the washing nitrogen which is cooled in said heat-exchanger of the gas decomposition plant by heat-exchange with a fraction withdrawn from said gas decomposition plant, said condensor being situated in said air separation plant and two connecting lines between said two plants, one connecting said heat-exchanger of said gas decomposition plant with said condensor and the other connecting said condensor with said nitrogen washer in the gas decomposition plant.

7. Apparatus as claimed in claim 6 comprising an expansion machine and a connecting line for passing a gaseous fraction withdrawn from said air separation plant and warmed in said condensor to said expansion machine.

References Cited in the tile of this patent UNITED STATES PATENTS 1,354,380 Crommett Sept. 28, 1920 1,723,425 Jaubert Aug. 6, 1929 1,843,043 Patart Jan. 26, 1932 2,417,279 Van Nuys Mar. 11, 1947 2,785,548 Becker Mar. 19, 1957 Notice of Adverse Decision in Interference In Interference No. 92,501 involving Patent No. 2,962,867, M. Seidel, PROCESS FOR DECOMPOSING HYDROGEN-CONTAINING GAS MIXTURES, final judgment adverse to the patentee was rendered May 4, 1965, as to claims 1, 2, 5 and 6.

[Ofiicz'al Gazette Sepember 28, 1965.] 

1. A PROCESS FOR THE DECOMPOSITION OF A HYDROGEN-CONTAINING GAS MIXTURE INVOLVING WASHING AT LEAST ONE DIFFCULTLY CONDENSIBLE COMPONENT OUT OF SAID GAS MIXTURE BY CONTACTING IT WITH LIQUID NITROGEN WHICH COMPRISES SIMULTANEOUSLY OPERATING A GAS DECOMPOSING PLANT OPERATING UPON SAID GAS MIXTURE AND AN AIR DECOMPOSING PLANT, WITHDRAWING NITROGEN FROM SAID AIR DECOMPOSING PLANT, COMPRESSING THE NITROGEN TO THE PRESSURE REQUIRED FOR SAID WASHING OPERATION, PRECOOLING THE COMPRESSED NITROGEN BY INDIRECT HEAT EXCHANGE WITH AT LEAST ONE FRACTION OF SAID HYDROGEN-CONTAINING GAS MIXTURE IN SAID GAS DECOMPOSING PLANT, FURTHER COOLING AND AT LEAST PARTIALLY LIQUIFYING SAID PRECOOLED NITROGEN BY INDIRECT HEAT EXCHANGE IN SAID AIRDECOMPOSING PLANT AND RETURNING THE RESULTING LIQUIFIED NITROGEN TO SAID GAS DECOMPOSING PLANT AND USING IT THEREIN AS THE WASHING LIQUID. 